This invention relates to aqueous pigmented inks for use in ink jet printers.
Ink jet printing is a non-impact method that in response to a digital signal produces droplets of ink that are deposited on a substrate such as paper or transparent film. Ink jet printing has found broad application for output for personal computers in the office and the home as well as in industry. There are several classes of ink jet printer, for instance thermal drop-on-demand printers, piezo drop-on-demand printers, and continuous ink jet printers.
Ink jet printers, particularly those for use in the home or office, generally use aqueous inks, and such inks commonly employ dyes as colorants. However the use of dyes introduces certain disadvantages, particularly the problems of poor light stability and poor fastness to washing and weathering of the prints produced. It is expected that these disadvantages can be overcome by the use of pigments as colorants in ink jet inks, and there is therefore considerable interest in such pigmented inks. The term pigment describes a colorant which is essentially insoluble in the aqueous ink medium. Various classes of pigment are catalogued and classified in the Pigments and Solvent Dyes section of the Colour Index International, published by the Society of Dyers and Colorists in 1997. Many pigments described by the Colour Index are suitable for ink jet use, together with certain compounds classified by the Colour Index as vat or disperse dyes as well as numerous other insoluble coloured compounds which are not included in the Colour Index such as, for example, the cyan pigments described in U.S. Pat. No. 4,311,775 to Regan.
Pigments need to be finely dispersed for use in inks, and this requirement is particularly important for use in jetting inks because of the fine nozzles used in ink jet printers. It is common to formulate dispersions of pigments for use in jetting inks by first dispersing the pigment in a suitable medium, frequently water, in the presence of one or more stabilizers to stabilize and disperse the fine particles, and then letting this dispersion down into the ink with more water, together with organic co-solvents and other additives. The stabilizer used in the dispersion is commonly known as a dispersant or surfactant, and the choice of this component is of crucial importance to the performance of the ink.
It is well known that the choice of dispersant will affect the particle size achieved during the dispersing operation as well as the ease of dispersion. It is also well known that the properties of the ink greatly depend on the stability of the dispersed particles, and the stabilization system is of crucial importance in achieving this. For example, it can be found that particles which are well stabilized in a concentrated dispersion lose this stability when let down into an ink, and that the particles in the ink flocculate or aggregate on storage. This can sometimes be due to simple dilution of the stabilizer, but can also result from interactions with the organic co-solvents or other additives which are commonly present in the final ink. However these co-solvents and other additives need to be present in the ink, either for it to be used successfully in an ink jet printer or to give acceptable properties to the final image. For instance, a major concern with all ink jet printing devices is pluggage of nozzles during operation and between operations, and it is common to add around 10 to 25% of a relatively involatile organic co-solvent or mixture of co-solvents to an aqueous ink to overcome this. Various simple aliphatic polyols, such as glycerol, ethylene glycol, propylene glycol, and diethylene glycol are known to be useful for this purpose. In addition, certain water soluble polymers are also known to be useful, generally in combination with low molecular weight organic cosolvents, and for instance U.S. Pat. No. 5,268,027 to Chan et al. describes the use of alkyl bis polyol ethers as pluggage inhibitors for dyed ink jet inks. However the presence of these additives can adversely affect the dispersion stability of pigmented inks.
It is also known that physical properties of an ink such as surface tension and viscosity which are important for achieving good jettability through an ink jet printer can also depend on the dispersant used in pigmented inks, as can kogation of the heating element for thermal printers. Finally such properties of the final image as density, sharpness, and smudge resistance also depend on the dispersant used.
Several dispersants useful for pigmented aqueous inks are already known. Those most commonly described are acrylic resins which comprise various copolymers of acrylic, methacrylic, or maleic acids, generally in combination with other vinylically unsaturated monomers such as styrene or acrylic esters, such as those described in U.S. Pat. No. 5,085,698 to Ma et al.; U.S. Pat. No. 5,172,133 to Suga et al. and U.S. Pat. No. 5,821,283 to Hesler et al. However with dispersants of this type it can be difficult to achieve the necessary ink stability in the presence of other additives and also to achieve the required viscosity and surface tension without adversely affecting the stability. Various ethoxylated surfactants such as alkyl phenol ethoxylates and alkyl ethoxylates have been described, for example in U.S. Pat. No. 5,837,044 to Santilli et al., but nozzle clogging with pigmented inks can be a problem with this type of dispersant. Simple surfactants, for example sodium dodecyl sulphate and sodium N-methyl-N-oleyl taurate as described in U.S. Pat. No. 5,651,813 to Santilli et al. are also known as dispersants in pigmented jetting inks.
However a need still exists for inks which are highly stable towards aggregation or flocculation on storage, which print successfully through an ink jet printer, and which give good properties to the final image, without introducing other disadvantages. We have found that pigmented ink compositions formulated using various sarcosinate compounds are particularly suitable for ink jet use.
The invention relates to a pigmented aqueous ink jet ink composition which comprises a sarcosinate compound of the formula:
xe2x80x83Rxe2x80x94COxe2x80x94NMexe2x80x94CH2xe2x80x94COOM
In which R is a ballasting group comprising at least ten carbon atoms and M is hydrogen, an alkali metal cation, an ammonium cation or a substituted ammonium cation.
Sarcosinate compounds are well known, and a variety of such compounds are commercially available. They may be prepared from sarcosine, which is an amino acid of natural origin, by acylation with a suitable acylating agent such as an acid chloride of the formula Rxe2x80x94COCl.
Particularly useful sarcosinate compounds are those in which the group R consists of an alkyl chain of between eleven and eighteen atoms. Other useful compounds are those in which the group R consists of an unsaturated alkyl group. It is to be understood that the group R may consist of mixtures of chain lengths or of different isomers in commercially available sarcosinate compounds.
Suitable alkali metal cations include sodium and potassium cations, and suitable substituted ammonium cations include ethanolammonium and triethanolammonium cations.
Specific examples of useful sarcosinate compounds which are commercially available include N-lauroyl sarcosine, N-cocoyl sarcosine, N-stearoyl sarcosine, Sodium N-lauroyl sarcosinate, Potassium N-lauroyl. sarcosinate, Sodium N-palmitoyl sarcosinate, Sodium N-myristoyl sarcosinate, Triethanolammonium N-lauroyl sarcosinate, Triethanolammonium Palm Kernel sarcosinate and Sodium N-oleyl sarcosinate. The oleyl group is an unsaturated alkyl group R and the cocoyl group is one in which the group R comprises a mixture of chain lengths.
The invention relates to pigmented ink jet ink compositions which are particularly suited for use in ink jet printers in general, and thermal ink jet printers in particular. The pigmented inks comprise an aqueous carrier medium, a pigment, and a sarcosinate compound, together with other components which are advantageously added to aqueous inks, such as surfactants, viscosity modifiers, and biocides. In addition, sequestering agents such as EDTA may also be included to eliminate deleterious effects of heavy metal impurities.
Specific examples of pigments for a black ink include carbon black (C.I. Pigment Black 7), such as furnace black, lamp black, acetylene black, and channel black, and o-nitroaniline black (C.I. Pigment Black 1), of which carbon black is preferred. Specific examples of the pigment for a coloured ink include C.I.Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 53, 55, 74, 81, 83, 93, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 151, 153, 154, 155, 180, and 185, C.I. Pigment Orange 5, 13, 16, 17, 34, 36, 43, 51, 70, and 71, C.I. Pigment Red 1, 2, 3, 9, 17, 22, 23, 31, 38, 48:1, 48:2, 48:3, 48:4, 49:1, 52:2, 53:1, 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 104, 105, 106, 112, 114, 122, 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 188, 190, 193, 202, 209, and 219, C.I. Pigment Violet 1, 3, 5:1, 16, 19, 23, and 38, C.I. Pigment Blue 1, 2, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17:1, 56, 60, and 63, and C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, and 36. Preferred examples of pigments for a coloured ink include Pigment Yellow 13, 74, 128, 151, 154, 155, and 180, Pigment Orange 34, 43, and 71, Pigment Red 122, 202, and 209, Pigment Violet 19, Pigment Blue 15:3, 15:4, and 16, and Pigment Green 7. It is also possible to mix more than one pigment in the inks of the invention.
Many of the above pigments are available commercially in finely divided forms which are specifically aimed at ink jet use. It is preferred to use such available forms in the inks of this invention. It is also possible to use processed pigments such as a graft carbon having a surface treatment.
The sarcosinate compounds are particularly useful as dispersants for pigmented ink jet inks. Therefore according to this preferred aspect of the invention, the ink is prepared by dispersing the pigment or predispersed pigment in the presence of the sarcosinate compound in water, together with optional co-solvents or other components, and then diluting this dispersion to form the ink. The dispersing step may be accomplished using one of several well known techniques, for example in a horizontal mini mill, a ball mill, an attritor, or by passing the mixture through a plurality of nozzles within a liquid jet interaction chamber at a liquid pressure of at least 1000 psi as described in U.S. Pat. No. 5,026,427 to produce a uniform dispersion of the pigment particles. By dilution, the ink is adjusted to the desired viscosity, colour, hue, saturation density, and print area coverage for the particular application.
The particle diameter of the pigment is preferably 10 xcexcm or less, particularly preferably 1 xcexcm or less.
The ink may contain up to approximately 30% pigment by weight, but will generally be in the range of approximately 0.1 to 15%, and is preferably approximately 1 to 8%, by weight of the total ink composition for most thermal ink jet printing applications.
The ink may contain up to 30% of a Sarcosinate compound, but preferably between 0.1% and 10%, and most preferably between about 0.5% and about 2% by weight, depending on the pigment used and other properties desired of the ink.
The aqueous carrier medium is water or a mixture of water and at least one water soluble organic solvent. Deionized water is commonly used. Preferably the aqueous carrier medium is a mixture of water and at least one water soluble organic solvent and most preferably a mixture of water with more than one water soluble organic solvent. Selection of a suitable mixture of water and water soluble organic solvent depends on the requirements of the specific application, such as the selected pigment, the desired surface tension and viscosity, the drying time of the pigmented ink jet ink, and the type of substrate onto which the ink will be printed.
Representative examples of water-soluble organic solvents that may be selected include:
(1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol;
(2) ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol;
(3) ethers, such as tetrahydrofuran and dioxane;
(4) esters, such as ethyl lactate;
(5) polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2, 4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol and thiodiglycol;
(6) lower alkyl mono-or di-ethers derived from alkylene glycols, such as ethylene glycol monomethyl (or -ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether, propylene glycol mono-methyl (or -ethyl) ether, triethylene glycol mono-methyl (or -ethyl) ether and diethylene glycol di-methyl (or -ethyl) ether;
(7) nitrogen containing organic compounds such as urea, pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and
(8) sulphur-containing compounds such as dimethyl sulphoxide and tetramethylene sulfone.
A preferred aqueous carrier medium is a mixture of water and at least one polyhydric alcohol such as diethylene glycol. Another preferred aqueous carrier medium is a mixture of water with at least one polyhydric alcohol together with at least one water soluble nitrogen containing compound such as urea or pyrrolidone. The aqueous composition may contain up to 50% of the organic cosolvent or cosolvents, but preferably up to about 10% of each of a mixture of organic cosolvents, and most preferably between about 5% and about 10% of each of a mixture of organic cosolvents.